According to cellular network systems, the entire area of coverage is divided into contiguous or overlapping cells having a size up to several kilometers depending on the anticipated traffic load. Each cell comprises a base station with a certain communication capacity or throughput capacity. Neighbouring cells use different frequencies, although cells that are further apart can use the same frequencies as they are not hindered by each other due to the relatively low power of all the transmitting stations used. Alternatively, some radio technologies like CDMA (Code Division Multiple Access) systems can use the same frequency in neighbouring or overlapping cells.
Different types of cells can be handled in the same geographical environment in a limited bandwidth. For example, there may be two different overlapping cell layers in one geographical region, which layers consist of micro cells and macro cells, respectively.
When a mobile station (MS) moves in such a cellular network while communicating via this network, handovers between cells in an area of the network have to take place. Moreover, while moving in the cellular network, the mobile station may move to a congested area consisting of at least one congested cell. In congested areas, however, the Quality of Service (QoS) offered to the mobile station may have to be reduced.
The WO 98 35514 A relates to a communication system which has the capability to transmit at high data rates and the ability to allocate the forward link resource to the users whenever requested, based on the availability of the resource. According this system, since voice communication cannot tolerate extensive delay, priority should be given to transmission of voice data over transmission of any data traffic. Moreover, since the amount of voice activity at any given moment is unpredictable, in the WO 98 35514 A it is suggested to continuously monitor the forward link and to dynamically adjust the data transmission so that the forward link capacity is not exceeded. Since the user may be in soft handoff between multiple cells, it is proposed to assign the data transmission based on the forward link capacity of each of the cells participating in the soft handoff.
Furthermore, the WO 98 45966 A is concerned with a method and an apparatus for scheduling data transmissions, in which a channel scheduler determines the maximum scheduling transmission rate for high speed data transmission. The maximum scheduled transmission rate is assigned at each scheduling period according to the availability of the reverse link capacity.